Surface topography and surface elemental composition analysis of Helixone, a new high-flux polysulfone dialysis membrane

Modern dialysis membranes need to fulfil two basic requirements. Firstly, the membrane structure, defined in terms of the size, structure and distribution of the pores at the inner separating layer of the membrane must be such that uraemic solutes of a defined molecular-weight range are selectively removed. Secondly, the physical and chemical properties of the blood-contacting surface must be such that minimal blood-material interactions take place that could either affect the functioning of the membrane, or, cause adverse reactions for the patient. A new polysulfone dialysis membrane, Helixone, has been developed specifically for the elimination of larger uraemic toxins using convective therapy modalities such as haemodiafiltration. The membrane is characterised by the nanoscale modulation of the innermost surface structures that lead to significantly increased sieving coefficients for molecules such as beta2-microglobulin, while maintaining the extremely low albumin removal property of the high-flux Fresenius Polysulfone membrane. A recent publication (Ronco C, Bowry SK. Nanoscale modulation of the pore dimensions, size distribution and structure of a new polysulfone-based high-flux dialysis membrane. Int J Artif Organs 2001; 24: 726-35) described the characterisation of the membrane of Helixone in terms of the membrane wall structure- and permeation-related parameters. In this paper, we describe the analysis of membrane surface parameters that influence the biocompatibility as well as the functioning of a membrane. The degree of roughness and the type of chemical groups of a blood-contacting surface are two of the main determinants of the biocompatibility characteristics of a membrane. The surface elemental composition of Helixone was determined using electron spectroscopy for elemental analysis (ESCA) while the surface topography of the membrane was evaluated using atomic force microscopy (AFM). The analysis showed that Helixone has an improved, smoother blood-contacting surface and retains the essential surface chemistry, and therefore the acknowledged biocompatibility profile, of the Fresenius Polysulfone membrane.